(d) force modeling error

(e) propeller shaft velocity (f) propeller shaft velocity error

Fig. 14. Experimental thruster control performance of closed loop

The matching results between simulation with experimental results show excellent correlation with only ±2N error in the entire space of thrust force under various ambient flow velocities and incoming angles. Note that the maximum force of the thrust is up to 50N. The results are also compared with conventional thrust models, and the matching performance with the proposed model is several times better than those of conventional linear ones.

Also in this article, the thrust force control performance of the proposed thruster model was examined. From the results in section 5, the best performance can be obtained by the open loop control with accurate model, because the thrust force cannot be measured directly. This means the force map from the propeller shaft velocity to thrust force plays important roll in control performance. The control performance with the model is acceptable for overall situation, which denoted normally less than ±3N control error.

7. Future works

The thruster modeling and control algorithm need to be enhanced in following aspects.

• Near dead-zone region modeling with complementary experiments

• Dead-zone controller

To precise dynamic positioning control of unmanned underwater vehicles, the dead-zone model and control algorithms should be developed.

8. References

Bachmayer, R. & Whitcomb, L. L. (2003). Adaptive parameter identification of an accurate nonlinear dynamical model for marine thrusters, J. of Dynamic Sys., Meas., and Control, Vol.125, No.3, 491-494. Bachmayer, R.; Whitcomb, L. L. & Grosenbaugh, M. A. (2000). An accurate four-quadrant nonlinear dynamical model for marine thrusters: Theory and experimental validation, IEEE J. Oceanic Eng., Vol.25, No.1, 146-159. Blanke, M.; Lindegaard, K.-P. & Fossen, T. I. (2000). Dynamic model for thrust generation of marine propellers, In: IFAC Conf. Maneuvering and Control of Marine Craft (MCMC'2000), pp. 23-25. Choi, S. K.; Yuh, J. & Takashige, G. Y. (1995). Development of the omnidirectional intelligent navigator. IEEE Robotics and Automation Magazine, Vol.2, No.1, 44-53. Fossen, T. I. & Blanke, M. (2000). Nonlinear output feedback control of underwater vehicle propellers using feedback form estimated axial flow velocity. IEEE J. Oceanic Eng., Vol.25, No.2, 241-255.

Healey, A. J.; Rock, S. M.; Cody, S.; Miles, D. & Brown, J. P. (1995). Toward an improved understanding of thruster dynamics for underwater vehicles. IEEE J. Oceanic Eng., Vol.20, No.4, 354-361.

Manen, J. D. V. & Ossanen, P. V. (1988). Principles of Naval Architecture, Second Revision, Volume II: Resistance, Propulsion, and Vibration, Soc. of Naval Architects and Marine Engineers, ISBN, Jersey City, NJ. Newman, J. N. (1977). Marine Hydrodynamics, MIT Press, Cambridge, MA. Saunders, A. & Nahon, M. (2002). The effect of forward vehicle velocity on through-body

AUV tunnel thruster performance. In: IEEE/MTS OCEANS '02, pp. 250-259. Whitcomb, L. L. & Yoerger, D. R. (1999a). Development, comparison, and preliminary experimental validation of nonlinear dynamic thruster models. IEEE J. Oceanic Eng., Vol.24, No.4, 481-494.

Whitcomb, L. L. & Yoerger, D. R. (1999b). Preliminary experiments in model-based thruster control for underwater vehicle positioning. IEEE J. Oceanic Eng, Vol. 24, No.4, 495506.

Yoerger, D. R.; Cooke, J. G. & Slotine, J.-J. E. (1990). The influence of thruster dynamics on underwater vehicle behavior and their incorporation into control system design. IEEE J. Oceanic Eng, Vol.15, No.3, 167-178.

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